1. Field of the Invention
The present invention relates to an imaging device having an electronic view finder.
2. Description Related to the Prior Art
Imaging devices such as digital cameras and digital video cameras, which obtain an image of a subject by causing an image sensor to capture the image of the subject formed by an image capture lens, have come into widespread use. Further, camera modules having an image capture lens and an image sensor are generally mounted on electronic devices such as smartphones, mobile phones, PDAs, and tablet terminals. Accordingly, the camera modules also function as imaging devices. In order to determine a photography area (composition) or perform a focusing operation, generally, a view finder is provided in such various imaging devices.
As the view finder, an optical finder that has a finder optical system or an electronic view finder (EVF) that displays an electronic image has been known. The electronic view finder includes a display section that is constituted of a liquid crystal display device and the like, and causes the display section to sequentially display live view images which are captured at a predetermined frame rate and are generated on the basis of imaging signals sent from the image sensor.
The live view display is performed by the electronic view finder through a plurality of kinds of signal processing. The signal processing includes reading of the imaging signal sent from the image sensor, generation of an image based on the read imaging signal, generation of an image to be displayed (i.e., live view image; hereinafter referred to as “display image”) which is formed using the generated image, and the like. In each signal processing, reading from a memory and writing processed signals into the memory are performed. Hence, it takes time to perform each signal processing. Therefore, a photographed image (an image acquired in response to an input of a photography instruction) is not completely displayed in real time, and generally an image, which is previous by one to several frames, is displayed with a delay. Hence, if a subject with a large motion is intended to be photographed, a photo opportunity may be missed.
In view of the above situation, recently, there is a known imaging device capable of performing live view display substantially in real time by not separately driving the image sensor and the display section, but driving those in synchronization at a predetermined phase difference and by restricting the display delay of the electronic view finder within a single frame period (US 2007/0211153 A1 corresponding to JP2007-243615A).
However, a field of view (a size of a displayed live view image) of the finder is one of the important factors that determine the usability of the finder. For example, if the live view image is excessively small, the image is less realistic. If the live view image is excessively large, it is necessary for a user to move a point of view location in order to view the entire image. Therefore, it takes time to check the image, and thus photo opportunity may be missed. Hence, as an imaging device employing a recent electronic view finder, there is a known imaging device capable of changing a display size of a live view image (JP2010-016669A)
When an electronic view finder is employed as a view finder of an imaging device, it is preferable that a display delay of a live view image is minimized and a display size of a live view image is set to be changeable. Hence, it can be considered that a technology of suppressing a delay of the display of a live view image according to US 2007/0211153 A1 and a technology of changing a display size of a live view image according to JP2010-016669A are used in combination. However, when the display delay is reduced in a method described in US 2007/0211153 A1, there is a problem in that the display size of the live view image cannot be reduced.
Specifically, in US 2007/0211153 A1, the display delay is minimized by sequentially displaying images of lines (lines of pixels of the image sensor), at which reading of the imaging signals is completed, on lines of display pixels corresponding one-to-one therewith without waiting for completion of reading of the imaging signals for each screen from the image sensor. As described above, when the image sensor and the display section are synchronously controlled, if the live view image is intended to be reduced in the display size and to be displayed at the center of the display screen, reading of the imaging signal at the last line (the lowest line of the live view image) of the image sensor is delayed in displaying.
Consequently, when the image sensor and the display section are synchronously controlled as disclosed in US 2007/0211153 A1, if the live view image is intended to be reduced and displayed, the image sensor and the display section are not synchronized. Thus, it is necessary to increase the display delay such that the time period of the reading of the imaging signals is appropriate for the timing of displaying the live view image.